Condenses



NOV. 1929. c. A. BIRCH-FIELD CONDENSER Filed Sept. 12, 1925 ATTORNEY Patented Nov. 26, 1929 UNITED STATES PATENT OFFICE CONDENSER Application filed September 12,-1925. Serial 1T0. 55,897.

My present invention relates to electrical apparatus and has particular reference to fixed condensers primarily suitable for telegraphic, or radio purposes and other similar 5 uses where capacities of small magnitude are re uired.

ondensers of this general type generally comprise a plurality of superposed layers of conducting material separated by some dielectric, the conductors and the dielectric being generally constructed of sheets of solid material such as'metallic plates and sheets of mica or the like. The capacitative magnitude-of such condensers depends upon the area and spacing of the metallic plates, and condensers of this character have generally been designed empirically, standard units of various capacities being constructed with differing areas and spacings. In general, adjustments are necessary upon the assembled device to produce the desired capacity, and these adjustments necessitate great care and delicacy if substantial uniformity in the condensers produced is desired.

It is an object of the present invention to provide a condenser of this character which is constructed. in a manner eliminating the disadvantages heretofore encountered and insuring uniform production without the necessity for delicate skilled adjustments.

A feature of my invention lies in constructing a condenser of materials which are readily 1 available on the market and in general of standard construction, rendering the manu facture of the condenser extremely inexpensive. v

More particularly, a feature of the mvention lies in providing a condenser by means of elongated conductors such as wiresof a standard size. The wires are spaced from one another and adielectric is interposed between them. Ina preferred construction the wire used is of a standard insulatedtype, and it is suitably coiled to provide a relatively large length within a small area, the insulation serving as the intermediate dielectric.

A particular feature of the invention lies in so coiling the wire that all possible selfand mutual inductance is\entirely neutralized; or, in other words, the distributed capacity of the coiled wire is utilized according to a predetermined plan to provide the capacitative efi'ect desired.

Another feature of the invention consists in novel structural means for mounting the wire and producing a completed article which will be compact, light, capable of being readily applied to a desired use, and presenting a neat outward appearance; and withal, rugged, reliable, and inexpensive.

For the attainment of the foregoin objects and such other objects as may ereinaf ter appear or be pointed out, I have illustrated several embodiments of my invention in the accompanying drawings, in which:

Fig. l is an exploded view of the structural elements of the device;

Fig. 2 is a side view in cross-section of the assembled device, including the conducting elements;

Fig. 3 is a diagrammatic view of a radio circuit, illustrating by way of example, a possible utilization of the condenser;

Fig. 4 is an enlarged plan View of a winding spool constituting an element of the device, the wire conductors being shown in exaggerated wound condition for the purpose of showing their relative dispositions; and

Fig. 5 is a diagrammatic view of a modified method of coiling the wires.

For the purpose of explaining the basic nature of the invention, reference will be had first to Fig. 4, in which the winding element 10, hereinafter referred to as the reel, is shown in plan view, with: the wire.elements whose distributed capacity is to constitute the con denser proper, shown in wound condition. One face of the reel is provided with radial slots 11 and 12 extending from the periphery to points short of the center, and preferably at an angle of a proximately 90 to each other. Two lengt s of standard wire, preferably bearing insulation material-of difierent configuration or color, are wound about the reel in the following manner. The two wires are laid next to each other, and one end 13 of wire No. 1 is made to project through. slot 11, and the corresponding end 14 of wire No. 2 is made to project similarly through slot 12.

The wires are then wound simultaneously in close proximity to each other until a desired length, depending upon the capacity required, has been Wound about the reel. Generally, I have found it preferable to utilize wire of a size and quality which will produce a capacity of .00025 microfarads per 80 ft. of length. After the required length has been wound, the opposite end 15 of wire No. 1 (distin guished by the color of the insulation) is brought through slot 11, and the corresponding end 16 of wire No. 2 is brought through slot 14. The wires will have been tightly wound, and the projecting of the ends through the slots 11 and 12 will serve to retain the tightly wound condition. It will be obvious thatthe original ends 13 and 14 of the Wires will project from the slots at points nearer to the center of the reel than the ends 15 and 16 because of the depth of wound wires. The reel will now be in condition ready for assen1- bly, and it will be observed that the condenser proper has been produced, comprising the conducting elements constituted by the wires and the intermediate dielectric constituted by the insulation about the wires.

The detailed construction of the reel 10 may vary considerably, depending upon requirements. Reference to Fig. 2 will illustrate a preferred method of construction, the opposite faces 17 and 18 being preferably disc shaped and retained in spaced relation to each other by a spacing washer 19, an eyelet 20 or other suitable fastening device passing through the washer 19 and engaging the discs 17 and "18.

Any suitable structural means may be provided for suitably mounting the reel 10, and I prefer to provide a casing comprising a base or body portion 21, and a cover portion 22 therefor. The portions 21 and 22 are preferably provided with openings 23 and 24 adapted to register with the eyelet 20, so that a suitable fastening'device, preferably an eye'- let 25, may be passed through the eyelet 20 and into engagement with the portions 21 and .22 simultaneously to retain the cover portion '22 and the reel 10 in position. The casin is provided with lateral lugs 26 preferably formed integrally with the body portion 21. These lugs carry conducting strips 27 which project through into the interior of the cats ing and are adapted to be electrically connected therein with the united opposite ends of each coil. I prefer to provide the lugs 26 with apertures 28, and the strips 27 with holes 29 adapted to register withthe apertures .28 so that suitable fastening devices such as eyelets 30 may be utilized for securing the strips 27 in position. I also prefer to provide the body portion 21 with an interior shoulder 31 against which the cover 22 may rest, and I prefer to construct the "lugs 26 in such a manner that when the strips are laid thereon, the exposed surface of each strip will be flush with the shoulder 31 to provide a smooth unbroken seat for the cover portion 22. I also prefer to construct the rim portion of the body 21, that is, the portion projecting beyond the shoulder 31, of a depth equal to the thickness of the cover 22, so that when the cover is placed into position against the shoulder 31, its outer surface will be flush with the outer edge of the body portion 21.

For the purpose' of facilitating electrical connection with opposite ends of each strip 27, I prefer to construct these strips with slots 32 or the like, according to requirements, and I prefer to make the strips 27 sufficiently long to project well into the interior of the casing, where the ends may be bent downwardly if desired, and to project laterally beyond the lugs 26.

The method of assembly of the device will be obvious from what has gone before. The method of constructing the condenser proper consists, briefly, in winding insulated wires into intercoiled relation, and electrically uniting the opposite ends of each wire. Thus, after the wires have been wound about the reel 10, and the opposite ends of each wire brought through and held by the slots 11 and 12, the wound reel is placed within the body portion 21; the strips 27 are then positioned upon the lugs 26, and the eyelets 30 inserted through the lugs and the strips in a well known manner and clamped to secure the strips in position. Thereupon the inner ends of the strips 27 are preferably bent inwardly a slight amount, and one set of wire ends is electrically connected, as by soldering, to one of said strips. More specifically the ends 13 and 15 (Fig. 4) might be attached to the inner end of one strip 27 and the ends 14 and 16 will then be attached to the inner end of the other strip 27; the cover 22 is then placed into position and the eyelet 25 is passed through the casing portions andthrough the reel 10 clamped in a well known manner to secure the entire device. If desired, the interior of the casing may be filled with paraffin or the like, before placing the cover in position.

The completed device is peculiarly'eflicient, light, compact and of a pleasing appearance.

The cost of manufacture is extremely small for the reason. that every element except the body portion 21 comprises a piece which is readily available uponthe market. The supporting member for the wire conductors is preferably constructed in the form of a reel as hereinbefore described, and its preferred method of construction necessitates only two disc washers, a spacing washer and an eyelet, all well known standard elements. Similarly, the eyelets 30 and 25 are inexpensive and readily available. The strips 27 comprise conducting strips of a well known type, and only very slight changes may be made therein tosuit requirements of design. The cover portion 22 consists of a small piece of insulating material such as that in well known use for panels and the like. The only specially made element of the present device is the body portion 21, and the preferred construction described, permits this element to be produced by a single stamping or casting operation.

I prefer to construct the elements forming the reel of insulating material such as fibre or hard rubber, and I prefer to construct the base portion 21 of material of the nature heretofore referred to with respect to the cover 22, but this construction is not essential, and the material may be varied to suit particular requirements or designs.

Inasmuch as the Wire conductors which are wound upon the supporting member 10 are of the standard size, I have produced a device which permitsof inexpensive manufacture of uniform condensers of all standard, and all special, capacities. Inasmuch as the wire is preferably of a very small size,

small lengths of it constitute negligible factors in the computation of the capacitative efl'ect produced. As a result, a large variety of condenser values can be easily manufactured without requiring any vital changes to be made in the structure as a whole. Larger condenser values would be manufactured by winding more coils of the very same wire about the reel, and smallercondenser values would correspondingly necessitate merely the reduction in the length of wire used. Moreover, this very same structural feature is of great importance in permitting accurate uniformity to result, because the wire is of uniform cross-section throughout, and the capacity produced is directly proportional to the length of wire used. Accordingly, certain standard lengths once predetermined may be usedctime and again and will produce condenser values of perfect uniformity. No skill is required, and no delicate adjustments are necessary for producin the desired result. Another advantage 0 the present construction lies in the constantly .fixed relation between the conductor and dielectric. The dielectric comprising the insulation is of uniform construction and is marketably available simultaneously with. the conductor. Another great advantage of the present 1nvention lies in the fact that moisture cannot affect the assembled device, and accordingly the capacity will remain invariable under all conditions.

It will be obvious that a particular feature of the invention lies in uniting the opposite ends of each conductor, thereby eliminating all possible inductance. Since a zero current will flow through each conductor because of its united ends, no inductive influence of one coil upon the other will be present.

Another advantageous feature directly resulting from the structureofthe present denals of the condenser.

utilized as fastening means only, and all.

vice lies in the possibility of making absolutely positive electrical connection between the wiring of the outside circuit and the termi- The eyelets 30 are electrical connection is made with the strips 27 which provide positive electrical connection to the wire elements within the casing. The provision of an eyelet 25 serves an added purpose in permitting the device to be attached to a panel or a baseboard or other fixed point independently of the electrical connections to the condenser. It is there fore not necessary in the present device to utilize the electrical connecting means for physical supporting purposes, and as a result, the device may be utilized for a great length of time without any strain being placed thereon, and in a manner which will permit of staunch and rugged mounting in desired position with respect to an outside circuit.

In Fig. 3 I have illustrated a possible use of the condenser, its coiled Wires being indicated diagrammatically by the reference numerals 33 and 34. Detailed description of the circuit'illustrated diagrammatically in Fig. 3 is deemed unnecessary, inasmuch as the device may be utilized in a vast number of instances which will be apparent to those skilled in the art.

In Fig. 5 I have illustrated diagrammatically a modified method of winding wires into intercoiled relationl In this construction, the wires are wound into a form of a figure 8 instead of being wound constantly in one direction about a reel.

- Though I have described my device as having utility within all ranges of capacity, I have found that my type of condenser in its preferred form is particularly suitable in a range from approximately .00025 to .001 microfarads.

It will be obvious that many other modifications and changes might be made by those skilled in the art withoutdeparting from the spirit and scope of the invention as expressed in'the a pended claims. And it is therefore intende that the details herein described and illustrated for the purpose of explaining the nature of my invention be interpreted as illustrative' merely, and not in a limited sense.

Having thus described my invention and illustrated its use, what I claim as new and desire to secure by Letters Patent is:

1. A condenser of the character described, comprising two coiled wire-like conductors, each of said conductors having its opposite ends electrically united, the united ends of one conductor forming one terminal of the con denser and the united ends of the other conductor forming the other terminal of the condenser, a supporting member therefor, a casing completely enclosingsaid member, and means for establishing electrical connection between said conductors and the outside of said casing, said means comprising a pair of: conducting strips extending into the casing at opposite parts thereof and electrically connected respectively With said condenser terminals.

2. A condenser of the character described,

comprising coiled Wire conductors, a sup porting reel therefor having an axial bore, a casing for the reel having openings adapted to register With said bore, and an eyelet passing through said openings and bore to hold the reel imposition.

3. A condenser of the character described, comprising coiled insulated Wire conductors, a reel therefor, a casing for said reel and having lateral lugs, and conductingstrips carried by said lugs and projecting into the interior of the casing and adapted to be electrically united With said conductors.

4. A condenser of the character described, comprising coiled conductors, a reel therefor, a casing for said reel and having apertured lugs, conducting strips projecting through said casing and adapted to be electrically united with said conductors, said strips having holes adapted to register with said apertures, an eyelets in said apertures for retaining said strips in position.

5. A condenser of the character described, comprising coiled conductors, a reel therefor, and a casing for said reel, said casing comprising a body portion, a cover portion, and means for simultaneously securing the cover portion and the reel in position.

6. A condenser of the-character described, comprising a pair of coiled Wire conductors, a supporting reel therefor, a casing for the reel, and means passing axially through the reel and through the casing for holding the reel in position.

In testimony whereof, signed my name.

QHARLES A. BIRCH-FIELD.

l have hereunto 

